1. Field of the Invention
The present invention relates to a tool changer that is disposed between a tool magazine and a tool spindle of a machine tool to perform exchange of tools, and also relates to a machine tool equipped with the tool changer.
2. Description of the Related Art
A conventional tool changer that is capable of automatically replacing a tool attached to a tool spindle of a machine tool with another tool prepared in a tool magazine, as disclosed in the Japanese Patent Laid-Open Publication No. Hei 8-141863, performs the exchange of tools by pulling, pushing, or rotating a changer arm shaft holding a tool that is driven, via a plurality of cams, by a motor or the like. However, this kind of tool changer requires a large cam box and accordingly the overall size of this apparatus becomes larger. Furthermore, because transporting a tool from a remote tool magazine to the tool spindle or vice versa is difficult, the tool changer must be disposed between the tool spindle of the machine tool and the tool magazine, and also disposed in close proximity to them. Accordingly, a heavy device must be disposed at an upper part of the machine tool, whereby the machine size is further increased.
To solve the above-described problem, Japanese Utility Model Publication No. Hei 8-4989 discloses, as shown in FIG. 12, a compact tool changer equipped with a servo motor for controlling a pulling/pushing motion of a changer arm shaft, and another servo motor for controlling a rotating motion of the changer arm shaft, without using a large cam box. As shown in FIG. 12, the rotations of two servo motors 212 and 213 are controlled by an NC apparatus for rotating and pulling/pushing a tool-changing arm 211. An arm shaft 209 has circumferential grooves 209b, functioning as a lifting or lowering rack, on its cylindrical surface formed at one end, and has a spline 209a formed at the other end. A pinion 225 meshing with the circumferential grooves 209b is driven (i.e. rotated) by the first servo motor 213. A pinion 210 meshing with a gear 218 is driven (i.e. rotated) by the second servo motor 212. The gear 218 has a female spline coupled with the spline 209a. However, like the above-described conventional tool changer, because transporting a tool from a remote tool magazine to the tool spindle or vice versa is difficult, this type of tool changer must be disposed between the tool spindle of a machine tool and the tool magazine, and also disposed in close proximity to them.
Meanwhile, tool changers have recently been required to perform long-duration, automated operation. To satisfy such a requirement, the tool changer must hold many replacement tools. However, according to the above-described conventional tool changer, structural restrictions require that the tool changer be disposed between the tool spindle and the tool magazine and also disposed in close proximity to them, making it difficult to increase the size of the tool magazine. Furthermore, attaching a plurality of tool magazines to the tool changer is also difficult. Thus, realizing a long-duration, automated operation is not easy.
If such a tool magazine capable of holding many tools is disposed far from the tool spindle, exchanging tools will require that the tool changer have an appropriate transporting mechanism to transport a tool, while the tool is held with the changing arm, from the remote tool magazine to the tool spindle, or vice versa. However, the above-described conventional tool changer has no capability of transporting tools between the tool spindle and the tool magazine.
Japanese Patent Laid-Open Publication No. Hei 9-131637 discloses a method for enabling a system to perform exchange of tools by transporting a tool from a remote, large-capacity tool magazine to a tool-changing position of a tool spindle. The apparatus proposed in this prior art document includes a tool-changing unit that performs both a pulling/pushing motion and a rotating motion of a tool-changing arm. The tool-changing unit can be shifted along a guide rail that is provided separately. Furthermore, as shown in FIG. 13, Japanese Utility Model Laid-Open Publication No. Hei 4-38335 discloses a tool-changing method including a step of picking up a tool with a sub-arm 323, without directly holding and transporting the tool from a remote tool magazine 309; a step of transporting a shift base 321, which carries the sub-arm 323, to a ready station 310 of the tool spindle; and a step of performing exchange of tools by means of a conventional tool changer between the ready station and a tool spindle 306.
The above-described tool changer that holds and transports a tool from a remote tool magazine to a tool-changing position is very large in size, and accordingly an enlarged space is required for installing this machine tool. Especially, such a large tool changer cannot be incorporated into a general combined machining apparatus or into a vertical-type machining center. Furthermore, if a mechanism for transporting a tool and a mechanism for exchanging the tools are provided independently, the entire structure of the system will become complicated, and the reliability and accuracy of operations will be lowered. Moreover, according to the above-described method using a ready station for performing exchange of tools, accomplishing this operation requires a relatively long time.
Because a conventional tool changer has been required to be disposed between tool spindle of a machine tool and a tool magazine, and also disposed in close proximity to them, the layout of constituent parts of the machine tool has been significantly restricted, and accordingly realizing a compact machine tool has been difficult. Furthermore, maintaining the tool changer clean has been impossible, because of difficulty in arranging the tool changer so as to usually be disposed outside a machining area and conveyed into this area only when the tool-changing operation is carried out.
It may be possible to modify a conventional tool changer so as to perform, as an integrated operation, both transportation and exchange of tools, if the changer arm shaft driven to perform rotating and pulling/pushing motions is extendable. However, when the changer arm shaft is used to hold and transport a tool from a plurality of tool magazines, a practically required pulling/pushing length of the arm will reach approximately 1 m. Such a long length will not be practically realized when structural restrictions of the tool changer are taken into consideration.
Furthermore, if a long-duration, automated operation is performed, a tool tip position may change due to wear and tear occurring during a machining operation. In such a case, after accomplishing the exchange of tools, the tip position of a replacement tool must be confirmed and corrected before the next machining operation with this tool is started. However, a conventional tool changer that cannot transport a tool has difficulty in incorporating such an operation as part of a sequential tool-changing operation. Thus, accomplishing the tool-changing operation requires a long period of time.